1. Field of the Invention
The present invention relates to a substrate for an ink jet printing head with fuse element that can be blown by passing an electric current therethrough, an ink jet printing head with the substrate, an ink jet printing apparatus using the ink jet printing head, and a method of blowing the fuse element of the ink jet printing head.
2. Description of the Related Art
A variety of types of printing apparatus, such as laser printers and ink jet printers, have been in use. An ink jet printer (ink jet printing apparatus) forms an image by ejecting ink droplets from a printing head. The ink ejection method includes an electrothermal conversion method (bubble jet system) that uses electrothermal transducers (heating elements). The ink jet printing head of the electrothermal conversion type holds a liquid ink in an ink holding unit comprising a nozzle, an ink supply path and an ink reservoir. The heating element in each nozzle is energized to form a bubble in the ink and an energy of the expanding bubble expels an ink droplet from the nozzle.
In a general serial scan type ink jet printer, the printing head capable of ejecting an ink is supported on a carrier mechanism so that it can be moved in a main scanning direction. To a position facing the printing head, paper as a printing medium is successively fed in a sub scanning direction by a paper feed mechanism. As the ink ejecting printing head and the surface of the printing medium are moved relative to each other in the main and sub scanning directions, the printing head ejects ink droplets according to print data. Ejected ink droplets land on and adhere to the surface of the printing medium to form a dot matrix image.
The ink jet printing head comprises, for example, a head substrate and a nozzle member, with a base of the head substrate having an ink ejection mechanism and others formed of various layered films. The ink ejection mechanism uses heating elements in the case of an electrothermal conversion type and piezoelectric elements in the case of an electromechanical type. Generally, on the surface of the base a driver circuit for driving the ink ejection mechanism and a data input portion for supplying print data to the driver circuit are also formed of a various layered films.
In recent years it has been proposed to mount a ROM (Read Only Memory) on the head substrate so that data, such as a printing head ID (Identity) code and a drive characteristic of the ink ejection mechanism, can be readably held in the ink jet printing head. For example, Japanese Patent Application Laid-open No. 3-126560 (1991) discloses a construction in which an EEPROM (Electrically Erasable Programmable ROM) is mounted on the ink jet printing head. The ink jet printing head disclosed in Japanese Patent Application Laid-open No. 3-126560 (1991), however, has the EEPROM mounted separately from the head substrate and thus its construction is complex, deteriorating productivity and making a size and weight reduction difficult. Another disadvantage is that although the existing ROM chip is useful when print data is large, it becomes a disadvantage costwise when the print data is small.
U.S. Pat. No. 5,504,507 and U.S. Pat. No. 5,363,134 disclose a construction in which a ROM comprised of fuse elements is formed in the base of the head substrate of the ink jet printing head along with the layered films of the ink ejection mechanism. In this construction, when the layered films such as the ink ejection mechanism are formed on the base during the process of manufacturing the head substrate, the fuse elements as the ROM can also be formed at the same time. By selectively blowing the fuse elements, the ROM can hold binary data according to the presence or absence of the fuses, or whether or not the fuses have been blown. The ink jet printing head using such a head substrate does not require a ROM chip to be prepared separately from the head substrate, thus simplifying the construction capable of readably holding a variety of data, improving the productivity and realizing reductions in size and weight.
The head substrate disclosed in U.S. Pat. No. 5,504,507 and U.S. Pat. No. 5,363,134 can readably hold various data of the ink jet printer through the fuse elements and have these fuse elements formed in the base along with various layered films. For example, as shown in FIG. 10, a fuse element 410, an interlayer insulating film 104, fuse electrodes 105, and a protective film (insulating film) and others are formed in layers in a predetermined shape on the surface of the base 101. Over the surface of the protecting film (insulating film) a nozzle member 107 is formed of an organic resin.
As a method of blowing such a fuse element 410, a laser beam method which electrically opens the fuse element 410 by blowing and evaporating it with a laser beam is most effective. This method, however, is not suited for mass production because a melted material produced when the fuse element 410 is blown adheres to the printed circuit board and because the fuse element blowing process makes this method costly. Another method that blows the fuse element 410 by applying a large electric current is not costly, with little melted material adhering to the printed circuit board. So, this method is suited for mass production.
Ink contacts the head substrate of the ink jet printing head. If, for example, the ink infiltrates into a portion where a fuse element was blown, that portion and electrodes may be corroded, deteriorating reliability. For this reason, the fuse elements fabricated in the head substrate at the same time that the board is fabricated must have a structure that enables the fuse elements to be blown reliably and prevents the ink infiltration.
In the method that applies an electric current to the fuse element 410 to blow it, since the fuse element is situated at the lower part of the layered structure, as shown in FIG. 10, the fuse material melted when it is blown may fail to scatter sufficiently. If the fuse element is blown and becomes electrically open, the open circuit may be closed again by the melted fuse material that exists in a narrow space.